Phthalimide N-oxyl (PINO) is a potent hydrogen atom transfer (HAT) catalyst that can be generated electrochemically from N-hydroxyphthalimide (NHPI). However, PINO is short-lived, which has caused a limited operational utility for methodology development due to PINO decomposition. Our group is interested in developing new strategies for selective oxidation using NHPI or similar species. One reaction of interest is the selective oxidation of native lignin, a problem which brought many inadequacies to the fact of high catalyst loading and long reaction time. We have described a comprehensive electroanalytical study of the NHPI/PINO redox couple, and have conducted computational studies to uncover the mechanisms by which PINO degrades. Previous efforts on designing PINO-derived HAT catalysts have largely focused on adjusting BDFEs to improve reactivity. In contrast, the identification of PINO decomposition mechanisms suggests a new viewpoint to advance NHPI-catalyzed electrochemical oxidations – at least two aspects (BDFE and decomposition) must be considered in concert to design more effective N-oxyl catalysts for C-H oxidation reactions. The design of such novel catalysts is currently under investigation.

Electrocatalytic lignin oxidation

ACS Spring 2022

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